Incoming trunk-line.



N0- 84l,339. PATENTEDJ'AN. 15, 1907.

H. M. POST.

INGOMING TRUNK LINE. APPLICATION FILED MAR.14.1906.

rue NORRIS PETERS cm, WASHINGTON, n. c.

UNITED STATES PATENT OFFICE. I

I-IOWARD M. POS'IIOF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGGS'WITOHBOARD- & SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A

CORPORATION OF ILLINOIS.

Specification of Letters Patent.

Patented Jan. 15, 1907.

Application filed March 14, 1906. Serial No. 305.993.

To all whom, it may concern:

Be it known that I, HOWARD M. PosT, a citizen of the United States,residing in Chicago, county of Cook, and State of Illinois, haveinvented a new Improvement in Incoming Trunk-Lines,-of which thefollowing is a specification. V

lWIyinVentionrel-ates to telephone trunk systems for making connectionbetween subscribers' whose lines terminate at diiierent switchboards andusually at switchboards located in ditterent central ofiices forexchanges and to signaling means between the operators and subscribersby means of which such a connection is made and the connectionsupervised during conversation.

such systems the opera/tors cord-circuit is usually employed foranswering the calls coming at the initiatory or Astation, and in-case asubscriber is desired whose line terminates at another exchange thecalling end of the operators cord-circuit is connected with the outgoingend oi a trunk-line which terminates in spring-jacks at the'A stationand a c-allingplu-g at the incoming end of the trunk-line or B station.It is usual to provide a battery at each of the exchanges -forcontrolling the signals between the operators in making and supervisingthe connection, the battery at the A exchange being used to furnishcurrent over the line to energize the. transmitter of the callingsubscriber and the battery at the B exchange to furnish current to thesubstation-transmitter of the called subscriber. Dueto the fact that thehattery at each exchange is fur: nishing current over the lineterminating at that exchange for talking purposes it is usual in suchsystems to sever the metallic trunk connection-between the subscribersto the flew of direct current and to inductively unite the circuit forthetransmissionof voice-currents by means of a repeating coil or by theuse of condensers inserted in the ta lking-strands of the trunk-line.The use of condensers or repeating coils to inductively unite the sidesof the trunk-circuit for conversation add to the cost of installationand reduce the ei Iiciency of the talking-circuit. Insuch systems alsoit is necessary to use a twenty-four-volt battery at 'both exchanges forenergizing the transmitters of the respective slrbscri'bers.

In my invention a complete metallic circuit is provided to thevoice-currents over the trunk-line from one exchange to the otherwithout the use of intervening in ductive means, such as repeating coilsor condensers, and the battery at the A ex change 18 adapted to furnishcurrent to the transmitters .of both the calling and thecalled-subscriber. The cost of installation is therefore materiallyreduced and the talkingcircuit is coincident with the battery-circuitfrom the A exchange over the trunk-line to the called subscribersstation.

In the accompanying drawings I have shown two subscribers linesterminating at different central oflices with an --operator"scord-circuit at the A exchange and a form of trunk-circuitembodying myinvention, which I have worked out for commercial purposes, extendingbetween the A exchange .1 and the B exchange 2. I

At the A exchange the subscribers line is shown consisting of limbs 3and 4E, terminating in contact-springs5 and 6 of the cut-ofi relay 7. Acall-bell 8 and condenser 9 are located in a permanent bridge of theline conductors, and [a transmitter 1 0 and receiver 11 are located in abridge of the line normally off relay when said relay is energized.v Theline conductor 4 is normally connected with ground by a back contact ofthe cut-off relay, and the line conductor is normally connected with oneside of the winding-of the line-relay 14 at another back contact of thecut-off relay, the other side of the winding :of

l the line-relay being connected with the cen:

tral-ofiice battery 15 by means of conductor 16. Multiplejacks 17 areprovided at the diiierent switchboard-sections.. The linerelay isadapted'to control through its normally open contacts the circuit of thelinesignal 18 in t'he usual manner.

1 The subscribers line entering the B exchange and itsswitchboard-section is shown the relay 50. The relay 72 has its. circuitnormally open at the front contact-74 of the relay 45 and has one side:of its Winding connected with saidcontact by means of conductor and theother side of its Winding connected with. the battery 51 by means ofconductors 76 and 63. A. ringing-genera tor .77 is adapted to beconnected between ground and the tip side of the line by the, op erationof the ringing-key49 to signal the subscriber, a normally open contact78 of the ringing-key being connected With-the live side of battery 51bymeans of conductor 79 to maintain the cut-.oif-relay ,7 actuatedduringthe operation of ringing.

In the operation of the system a subscriber Whose line terminates atexchange 1 signals the operator by removing telephone from the hook, 1apathfor 'currentbeing thereby closed from thebattery 15 over conductor16 through the line-relay 14,-the limbs of the telephone-line, includingthe substation ap. paratus, and to ground. atthenormally closed contact5 of the cut-off relay .7. The.li=.1e-. relay responsive to current inthis. path Will attractits armature and. light the line-lamp 18. Uponseeing the signal the operator Will insert a plug of her @cordecircuitin the answering-j ack of the line closing a path for current from. thebattery 15, through the of supervisory relay 23, the sleeve'-. contactsof the inserted .plug; and jack, through the cut-off relay 7 to ground.The cut-off relay will attract its armature 5 and 6, removing thegroundv from the tip side of the line. and retiring the line-signal bybreak.- ing the connection with the line-relay upon the sleeve side ofthe line, at the same time connecting the external limbs of thetelephone-line with. the jack-section thereof at the front contactsof-said relay. The circuit of. the supervisory lamp 27 Will be closed atthe contacts of relay 23 by current in this path;- but due. to thefactthat the subscrihers receiver is off its hook ,a. path for current iscompleted through the substation talk ing. apparatus .overthe tip side:ofthe line, the tip-contacts of the jack and plug, tip-strand 19, andthrough the Winding of the supervisory relay 24'to battery, thus openinga circuit of the supervisory lamp 27 at the normally closed .contactsofsaid relay and pre venting the operation of said signal. The operatorwill then throwher listening-key 3.5 to ascertain the number of thesubscriber d-e sired. Upon learning that a subscriber Whoselineterminates at station 2 is desired the operator will depress, herorder-Wire key 39 and communic-atethe number of the sub seriber desiredto the B operator, who Will tell the A operator What trunk-line to usein making the connection. The A operator will then insert her.calling-plug in a jack of the designated line. A pathfor current willthen be closed from the battery 29 through With the test-relay32. rentwill also flow from the branch containing the impedance-coil 47, overtrunk-conductor 41, armature 43 of relay 45, through the supervisoryrelay 29", sleeve-strand 21 of the cordcircuit, the sleeve contacts ofthe inserted plug and jack, and the Winding of 28 and will connect thenorm-ally severed portions \of the tip-strand for conversation by meansof its armature .31, severing the .connection of the calling end of thetip-strand A portion of this curthe- Winding of .the high-resistancetrunkrelay .46., armature 44 of relay 45., trunk-conductor 42,tip-contacts of the plug and jack,

tip-strand 1 9 of the cord-circuit, and the windj ing of the tipsupervisory relay30 to battery.

The tip supervisory relay 30 does not attract its armature by current inthis path, due to l the high-resistance of the trunk-relay 4'6, the

trunk-relay being preferably of fifteen-thousand ohms resistance .andthe tip supervisory relay 10f one-hundred ohms. The supervisory signal:28 Would therefore be lighted throughthe closedcontacts of bothsupervisory relays to notify the A operator that the called subscriberhas not yet responded. The trunk-relay 46 is enerziged by this flow ofcurrent attracting its armature and closing the circuit of' the guard ordisconnect lamp 62,.from the live side of battery 51 over conductor 63,through the lamp 62, conductor '64, and front .contact. of relay 46,conductor54, and the armature 53 of relay 50 to ground. The signal. 62will therefore be lighted to notify the B operator that the Aoperatorhas inserted her calling-plug in a jack of the propertrunk-line. The B operator, if she has not previously done so, will thentest the condition of the Wanted line in'the usual manner. If the lineis busy, a potential above that of ground Would exist at thesleevecontact of the j ack due to a flow of battery through the cut-oif relay7 of the line at the switchboard-section Where such connection exists.As the tip-strand of the operators testing-terminal is normally groundedthrough the test relay 56, a flow of current Will'I'GSIlli? over thetip-strand 57 and the Winding of the test-relay56 to ground. Thearmature 58 of the test-relay Will close a path for cur rent from. thebattery 51 through. the, tertiary Winding of the operatorsinduction-coil, jincludingconductors .63, 76, 76?, and .59. Current inthis path will produce aninductive click in the operators head-receiverto notify her that the line is busy. If the line is not in use, noflowof current Will result and the op erator will insert hercalling-plug into the jack of the desired line. Current will then flowfrom battery 51 over conductors 63., 80, and 5.2., through the Windingof relay 50, sleeve-contacts of the plug and jack, and

through the Winding of the'cut-ofif relay 7 to ground. The relay 50 willattract its armatures, severing the connection of the testrelay with thetip-strand and uniting said strand for conversation at its armature 55,and opening the circuit of the guard-lamp 62 and closing the circuit ofthe rin ing-lamp 69 at its armature 53.v The guardamp 62 will thereby beeiiaced and the ringing-lamp 69 lighted, the circuit of the-lattersignal being traced from battery 51 over conductors 63, 80, and 70,through the lamp 69, normally closed back contact 71 of relay 72,conductors 73 and 68, and contact-armature 53 of the relay 5O torground.The flowpf current through the cut-off relay will remove the connectionof the line-relay 14 with line conductor 3 at contact-spring 6 of thecut-off relay to prevent the operation'of the linesignal 118 and willremove the ground connection from line conductor4 at contactspring 5 ofsaid relay. The operator will then signal the subscriber by operatingher ringing-key 49, signalingcurrent flowing from the generator 77overthe tip-contacts of the plug and jack, line conductor 4 through thesubstation signaling apparatus, line conductor3, sleeve-contacts of thejack andplug,

. sleeve-strand 49, back contact 78 of the ringingfkey, conductor 79 andto ground through thebattery 51'. During theprocess of ringing thecut-off relay -7 is maintained actuated by current from the battery 51over conductor 79, contact 78 of the ringing-key, sleeve contacts of theplug and jack, and through the winding of said relay to ground.

Upon the response of the called subscriberthe relay is operated over apath for current which-maybe traced'frombattery 51 over conductors 63,-80, and {52, the Winding of relay 50, sleeve-contacts of theplug andjack, lineconductor 3, the substation talking apparatus, line "conductor4, thetip-cont acts of the jack-and plug, tipestrand 47, and

through the Winding of the relay 45 to ground. The rel ay. 45 attractsits armatures, opening the circuitof. the high-resistance trunk-relay46. and extending the circuit-of battery 29 at the A exchange from thearmature 43 of the relay45-to the armature 44,.of-saidrelay, over thesleeve-strand 48 of thetrunk-cord, sleeve contacts ofthe plug and jack,limb 3 of the telephone-line, substation talking apparatus, limb 4 ofthe telephone-line, the tip-contacts of the jack and plu and cord-strand47 to the armature 44 of t e relay 45. It Will thus be seen that thetelephone-line of the called subscriber is substituted in the path ofcurrent from the battery 29. at the A exchange for the high-resistancetrunk-relay 46 and that the battery 29 is thus utilized for furnishingenergy to the transmitter at the called subscribers station over ametallic line free from inductive devices or repeating-coils of any kindand free from impedance, the conducsaid relay, retiring said si nal andnotifying the A operator that the ca led subscriber hasv responded. v

The operation of the relay 45 opens the cir- 66 of said relay and closesthe circuit of the relay72 at its front contact 74. The guardlamp 62 istherefore prevented from lighting when its circuit is closed at the backcontact of the trunk-relay 46, and said signal remains dark. Theringing-lamp. 69'is extinguished by the'operation of the relay 72, dueto current from the battery 51 over conductors 63 and 76, the winding ofthe relay 72, conductor 75, contact74 of relay 45, conductors 67 and 68,and armature 53 of relay 50 to ground. The circuit of the ringing-lamp69 is broken at the back contact 71 of relay 72 and the ringing-lampextinguished. A locking-circuit is also completed for the relay 72fromthe battery 51 over conductors 63 and 76, the winding of said relay,front contact 71, conductors 73 and 68, and armature 5.3

of the relay 50 to ground. I

; cuit of the guard-lamp 62 at the back contact At the termination oftheconversation,

when the subscriber at the A exchangehangs up his receiver, the circuitthrough thesupervisory relay 24 is opened, denergizing said relay andpermitting its armature 26 todrop back, closing the circuit of thesupervisory lamp 27, thus notifying the operator that this subscriberhas returned ,hisreceiver to its hook. The return of the subscriberstelephone to its hook at the B exchangeopen's the circuit through therelay45, permitting its armatures 43 and 44 to drop back, inserting thehigh-resistance trunk-relay in'the path of current from-battery 29 attheA exchange. As previously stated, the resistance in this path issufiicient to prevent the operation of the tip supervisory relay30,'Wl.'li0l1 releases its armature, closing the circuit of the supervisory signal 28, which is illuminated to notify the operator that thesubscriber at the B exchange has returned his receiver to its hook.

It will be noted that the ringing-lamp 69 will not be lighted when the Bsubscriber hangs up his receiver, due to the locking-circuit of therelay 72 above described. The disconnect-lamp 62 will also remain dark,due to the fact that its circuit is opened at the back contact of thetrunk-relay 46. When the A operator receiving the signal fordisconnection from both subscribers removesthe plug from the trunk-jack,the trunk-re-' III from the jack of the called subscriber, restoring allparts to normal condition.

It will be understood that the several grounds mentioned in connectionwith the exchanges maybe one and the same or the common ofiice returnand that the ground connection between the exchanges is to be Iconsidered the equivalent of a metallic conductor. l Vhere a metallicconductor is used, the danger of disturbing earth currents, which insome localities might be present in the exchange, due to the groundconnection,

. will be obviated.

Having described my invention, what I claim as new, and desire to secureby Letters Patent, is

1. The combination with a trunk-line, of a cord-circuit at the Aexchange to connect with the out oing end thereof, and a called-vsubscribers line terminating at the B exchange with which its incomingend is adapted to be connected, a supervisory relay associated'with thecord-circuit energized over .a circuit local to the A exchange when aconnection is made with the trunk-line, a signal having its circuitclosed by said relay, a second relay forcontrolling the circuit of saidsignal at another point, a trunk-relay in series with said second relayand of sufiiciently high resistance to prevent its operation, and meanswhen the called-subscriber answers for substituting thecalled-subscribers line in the circuit in place of said trunk-relay,whereby said second relay is actuated and said signal extinguished,substantially as described.

2. The combination with a trunk-line, of a cord-circuit at the Aexchange to connect with the outgoing end thereof, and acalledsubscribers line terminating at the B exchange with which itsincoming end is adapted to be connected, a supervisory relay associatedwith the cord-circuit energized over a circuit local to the A exchangewhen a con nection is made with the trunk-line, a signal having itscircuit closed by said relay, a second relay for controlling the circuitof said signal at another point, a trunk-relay in se ries with saidsecond relay and of sufficiently high resistance to prevent itsoperation, a relay at the B exchange energized by current over thecalled-subscribers line, said relay being adapted to remove saidtrunk-relay from the circuit and substitute the resistance of thecalled-subscribers line therefor, to energize said second relay andextinguish said signal, substantially as described.

3. The combination with a trunk-line, of a cord-circuit at the Aexchange to connect with the outgoing end thereof, and acalledsubscribers line terminating at the B exchange with which itsincoming end is adapted to be connected, a supervisory relay associatedwith the cord-circuit energized over a circuit local to the A exchange,when a connection is made with the trunk-line, a signal having itscircuit closed by said relay, a second relay for controlling the circuitof said signal at another point, a trunk-relay in series withsaid-second relay and of sufliciently high resistance to prevent itsoperation, and means when the called subscriber answers for substitutingthe called-subscribers line in the circuit inplace of saidtrunk-relay,whereby said signal is extinguished, and a path for direct current isclosed from one exchange to the other including the called-subscribersline, substantially as described.

4. The combination with a trunk-line, of a cord-circuit at the Aexchange to connect With the outgoing end thereof, and acalledsubscribers line terminating at the B exchange with which itsincoming end is adapted to be connected, a supervisory relay associatedwith the cord-circuit energized over a circuit local to the A exchangewhen a connection is made with the trunk-line, a signal having itscircuit closed by said relay, a second relay for controlling the circuitof said signal at another point, a trunk-relay in series with saidsecond relay and of sufliciently high resistance to prevent itsoperation, and means when the called subscriber answers for substitutingthe called-subscribers line in the circuit in place of said trunk-relay,whereby said signal is extinguished, and a path for direct current isclosed from one exchange to the other including the called-subscribersline, the path for voice-currents from the A exchange to thecalled-subscribers station being coincident with said direct currentpath, substantially as described.

5. The combination With a trunk-line, of a cord-circuit at the Aexchange to connect with the outgoing end thereof, and acalledsubscribers line terminating at the B exchange withwhich itsincoming end is adapted to be connected, a supervisory signal associatedwith the outgoing end of the trunk, means for closing the circuit ofsaid signal when a connection is made with the trunk, a supervisoryrelay for opening the circuit of said signal, a trunk-relay ofsufliciently high resistance to prevent the operation of saidsupervisory relay when connected in series therewith, and means when thecalledsubscriber' answers for connecting the calledsubscribers line inthe path of current from the A exchange and removing said trunkrelaytherefrom to actuate said supervisory relay and extinguish said signal,substantially as described. i

6. The combination with a trunk-line, of a cord-circuit at the Aexchange to connect with the outgoing end thereof, and acalledsubscribers line terminating at the B exv change with which its,incoming end is adapt-ed to be connected, a supervisory signalassociated with the outgoing end of the trunk, means for closing thecircuit of said signal when a connection is made with the described.

7. The combination with a trunk-line, of a cord-circuit at the Aexchange to connect with the outgoing end thereof, and acalledsubscribers line terminating at the B exchange with which itsincoming end is adapted to be connected, asupervisory signal associatedwith the outgoing end of the trunk, means for closing the circuit ofsaid signal when a connection is made with the trunk, a supervisoryrelay for opening the circuit of said signal, a trunk-relay ofsufficiently high resistance to prevent the operation of saidsupervisory relay when connected in series therewith; and a relayenergized over the called-subscribers line for connect ing said line inthe path of current from the A exchange and for removing said trunkrelay therefrom, whereby the resistance of the .path is reduced, andsaid supervisory relay actuated to extinguish said signal, substantiallyas, described. t r

8. The combination with a trunk-line, of

a. cord-circuit at the A exchange 'to connect with the outgoing endthereof, and a-calledsubscribers line terminating at the B ex; changewith which .its incoming-end; is adapted to be connected, a supervisorysignal associated with the outgoing end of;.th e 1 trunk, means forclosing the circuit of said signalwhen a connection is made with-thetrunk, a supervisory relay. for opening-the circuit of sald signal,'atrunk-relay of sufficiently high resistance to revent the operation ofsaid supervisory re ay when connected in series therewith, a relayenergized over the called subscribers line for connecting said line inthe path of current from the A exchange and forremoving said trunk-relaytherefrom, whereby the resistance of the path is reduced and saidsupervisory relay actuated to extinguish. said signal, and adisconnectelamp having its circuit normally closed at the contacts ofsaidtrunk-relay, andat the contacts of said relay adapted tor-beenergized over the called-subscribers line, substantially as described.

Signed by me at Chicago, county of Cook,

and State of Illinois, in the presence oftwo witnesses.

, HOWARD M. POST. Witnesses: A

' (LB. CAMP,

O. C. BRADBURY.

